The present invention relates to a method and apparatus for producing molten puddles in the course of scarfing.
The rolled metal is known to have all kinds of defects, such as slivers, cracks or hair-line cracks, etc. These flaws lead to a higher rate of metal consumption required for the manufacture of various products and adversely affect their quality.
An ever increasing volume of rolled stock production as well as stringent requirements imposed on the quality of metal call for the necessity to eliminate such defects.
There is known a method and apparatus for producing the molten puddle during scarfing as described in Czechoslovak Pat. No. 117,390.
The apparatus according to the patent referred to above includes a burner with ducts for supplying a fuel gas and oxygen. The burner is equipped with a folding-back device for prompt ignition of metal, made in the form of a bracket whose one end has a non-consumable electrode cammed therein, the other end thereof being articulated to the burner. In carrying out spot scarfing of randomly located defects, the electrode is fed to a spot at which the scarfing reaction is to begin until it comes in contact with the surface of a metal workpiece being scarfed. An electric current is then passed through the electrode to produce an electric arc between the metal and the electrode. Under the effect of the arc the metal is caused to melt at this spot and a molten puddle is formed on the metal surface. Thereafter, the scarfing operation is commenced by feeding a fuel gas and oxygen while the power supply is concurrently cut off and the electrode is removed.
The scarfing reaction on the surface of cold metal and the formation of the molten puddle take place instantaneously within a fraction of a second. However, this method requires additional power sources, as well as auxiliary equipment for feeding electric current to the electrode and the metal workpiece being scarfed.
U.S. Pat. No. 3,966,503 describes a method for making an instantaneous scarfing start, wherein a ferrous metal wire is brought in contact with a preselected spot on the surface of a metal workpiece. Then, an oblique heating flame, produced by a flow of fuel gas and a low intensity flow of oxygen gas, is directed at the metal surface slightly behind said spot located in the scarfing area. Impinging upon the metal surface, the heating flame is deflected upwardly, whereby the end of wire is heated to ignition temperature in an oxygen atmosphere. When the defective spot on the mobile metal workpiece being scarfed comes in contact with the hot end of the metal wire, a high intensity flow of scarfing oxygen is impinged upon said spot on the work surface. The scarfing oxygen flow is directed at an angle to the metal surface behind the defective spot or at the boundary of the scarfed area along its travel. The end of wire is melted, thereby causing a molten puddle to form in the scarfing area. To prevent its melting, the wire is retracted, while a high intensity oxygen jet causes the puddle to grow to its full width very rapidly. Thereafter, the supply of oxygen is discontinued.
The apparatus for carrying out the above method is described in U.S. Pat. No. 3,991,985. It comprises a means for feeding a ferrous metal wire and for contacting a preselected spot on the metal workpiece being scarfed with the end of said wire, a means for retracting the wire after the molten puddle has been formed on said surface, and a means for producing a flame for heating the end of said wire to its oxygen ignition temperature. The means for producing a heating flame includes ducts for feeding a fuel gas and oxygen. Interposed between said ducts is a duct for supplying a scarfing oxygen (a high intensity flow of oxygen). Although the above-described method requires no power sources, it fails to make fully efficient use of the heating flame, which gives up some of its heating power to the scarfed metal. Therefore, it takes as long as 1.5 sec for the scarfing reaction to take place on the metal surface. This being quite a long period especially where selective scarfing of cold metal workpieces is to be carried out. As a result, the productivity and reliability of the scarfing process are impaired.
In addition, the molten metal of wire is utilized inefficiently since the heating output of the melted wire is distributed over an extended area on the work surface. Moreover, because of irregularities on the surface of the metal workpiece, the deflected heating flame is spread uniformly over the height and width of said surface. Furthermore, by heating the end of wire in the heating flame deflected from the surface of the metal workpiece, it becomes impossible to make an instantaneous scarfing start and, consequently, to carry out the scarfing operation within a distance of 100 to 150 mm from the fron edge thereof.